The technical portion of the work of an optician consists in mounting a pair of correcting ophthalmic lenses in an eyeglass frame selected by a wearer.
Such mounting comprises three main operations:                acquiring the shape of a longitudinal profile representative of the shape of the outline of one of the surrounds of the selected eyeglass frame;        centering the ophthalmic lens in question, which operation consists in positioning and orienting said longitudinal profile appropriately on the lens so that once the lens has been machined to have this profile and has been mounted in the frame, it is positioned and oriented correctly relative to the corresponding eye of the wearer, thereby performing as well as possible the optical function for which it is designed; and then        shaping the lens, which operation includes a roughing step to bring its initially circular outline to a shape that is close to the desired shape, a finishing step, and a super-finishing step (polishing, beveling, . . . ).        
For half-rimmed eyeglass frames, the surround comprises a half-rim that fits over a top portion of the outline of the lens and a nylon string that runs along the bottom portion of the outline of the lens in order to hold the lens in contact with the half-rim. The finishing step then generally consists in grooving the edge face of the lens so as to form an engagement groove suitable for receiving not only the nylon string, but also a ridge provided along the inside face of the half-rim.
It is sometimes found that, once assembled, such half-rimmed eyeglass frames are not completely rigid and there is a risk of one or other of the lenses disengaging from the eyeglass frame. To mitigate that lack of rigidity, document EP 1 266 722 discloses a method of shaping an ophthalmic lens in which the finishing step includes a first grooving operation performed in a top portion of the outline of the lens, and a second grooving operation performed in a bottom portion of the outline of the lens to a different depth, thereby retaining the nylon string better.
At present, other types of eyeglass frames having mixed surrounds are appearing on the market.
For example, eyeglass frames are known in which each surround includes an interruption. The step of finishing the lens then comprises a first operation of beveling a major portion of the outline of the lens, and a second operation of leveling the edge face of the lens using a circularly cylindrical grindwheel in the interruption of the surround.
Half-rimmed eyeglass frames are also known that are unusual in which the inside face of each half-rim does not include a ridge, but rather an engagement groove. The step of finishing the lens, as described in document EP 1 266 722 then includes a first operation of beveling a top portion of the outline of the lens, followed by an operation of grooving a bottom portion of the outline of the lens.
The major drawback of those shaping methods, in which the finishing steps comprise two distinct operations, is that the boundaries between the two portions of the outline of the lens form unsightly discontinuities, since they can be seen at the ends of the half-rim (or of the interrupted surround).
For the above-described unusual half-rimmed eyeglasses, those discontinuities also present problems with holding the lens in its surround.